Multi-mixer system and method for reducing interference within multi-mixer system

ABSTRACT

A multi-mixer system includes an amplifier module and a plurality of channels. The amplifier module is arranged for receiving signals from an antenna or antenna arrays to generate a plurality of radio frequency (RF) input signals. The plurality of channels are coupled to the amplifier module, wherein the plurality of channels receive the RF input signals, respectively, and each of the channels includes a mixer for mixing one of the RF input signals with a local oscillating signal to generate a mixed signal. In addition, at least one of the channels includes an interference reduction circuit positioned between the amplifier module and the mixer.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of the co-pending U.S. application Ser. No.15/163,687 (filed on May 25, 2016), which claims the benefit of U.S.provisional application 62/188,107 (filed on Jul. 2, 2015). The entirecontent of the related applications is incorporated herein by reference.

BACKGROUND

In a multi-mixer system, a local oscillating signal used by a mixer maybe coupled to others mixer, causing interference to the other mixers. Ina multi-mixer system, there're more than one operating mixer and thelocal oscillating signal and its harmonics of one of the mixers can bean interference of other mixers. The interference can result in ade-sensitization of a receiver and results in unsatisfied signal qualityin a communication system. Therefore, how to provide an interferencereduction mechanism to lower the interference between mixers is animportant topic.

SUMMARY

It is therefore an objective of the present invention to provide amethod for reducing interference within a multi-mixer system, to solvethe above-mentioned problem.

According to one embodiment of the present invention, a multi-mixersystem comprises an amplifier module and a plurality of channels. Theamplifier module is arranged for receiving signals from an antenna togenerate a plurality of radio frequency (RF) input signals. Theplurality of channels are coupled to the amplifier module, wherein theplurality of channels receive the RF input signals, respectively, andeach of the channels comprises a mixer for mixing one of the RF inputsignals with an local oscillating signal to generate a mixed signal. Inaddition, at least one of the channels comprises an interferencereduction circuit positioned between the amplifier module and the mixer.

According to another embodiment of the present invention, a method forreducing interference within a multi-mixer system is provided, where themulti-mixer system comprises an amplifier module and a plurality ofchannels. The amplifier module is arranged for receiving signals from anantenna to generate a plurality of radio frequency (RF) input signals.The plurality of channels are coupled to the amplifier module, whereinthe plurality of channels receive the RF input signals, respectively,and each of the channels comprises a mixer for mixing one of the RFinput signals with a local oscillating signal to generate a mixedsignal. In addition, at least one of the channels comprises aninterference reduction circuit positioned between the amplifier moduleand the mixer. The method comprises: reducing an interference of theoscillating signal between the amplifier module and the mixer.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a system according to one embodiment ofthe present invention.

FIG. 2 shows two examples of the interference reduction circuit.

FIG. 3 shows three examples of the interference reduction circuit.

FIG. 4 shows that the harmonics of the oscillating signal LO2 arefiltered or isolated from the channel 120_1.

FIG. 5 shows some specific conditions that the harmonics of theoscillating signal LO2 may affect the operations of other channels.

FIG. 6 shows the detailed structure of the amplifier module according toone embodiment of the present invention.

FIG. 7 shows the detailed structure of the amplifier module according toanother embodiment of the present invention.

FIG. 8 is a diagram illustrating a system according to one embodiment ofthe present invention.

DETAILED DESCRIPTION

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, manufacturers may refer to a component by different names.This document does not intend to distinguish between components thatdiffer in name but not function. In the following discussion and in theclaims, the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” The terms “couple” and “couples” are intended tomean either an indirect or a direct electrical connection. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections.

Please refer to FIG. 1, which is a diagram illustrating a system 100according to one embodiment of the present invention. As shown in FIG.1, the system 100 comprises at least an antenna 102 (or an antennaarray), an amplifier module 110 and a plurality of channels 120_1-120_N,where the channel 120_1 comprises an interference reduction circuit122_1 and a mixer 124_1, the channel 120_2 comprises an interferencereduction circuit 122_2 and a mixer 124_2, and the channel 120_Ncomprises an interference reduction circuit 122_N and a mixer 124_N. Inthis embodiment, the system 100 may be a Long Term Evolution (LTE)receiver.

In this embodiment, the system 100 is a receiver or a transceiver, andis arranged to receive radio frequency (RF) signal from the antenna 102to generate at least one mixed signal (e.g. intermediate frequency (IF)signal) for further processing. In detail, the amplifier module 110receives a signal from an antenna to generate a plurality of RF inputsignals Vin1-VinN, and the mixers 124_1-124_N mix the RF input signalsVin1-VinN with oscillation signals LO1-LON to generate IF signalsVout1-VoutN, respectively. In FIG. 1, the oscillation signals LO1-LONhave different frequencies.

In the system 100 shown in FIG. 1, each of the interference reductioncircuits 122_1-122_N is arranged to reduce harmonics from the mixerwithin the same channel to other channels. For example, the interferencereduction circuit 122_1 is arranged to reduce harmonics from the mixer124_1 within the channel 120_1 to the other channels 120_2-120_N, . . ., and the interference reduction circuit 122_N is arranged to reduceharmonics from the mixer 124_N within the channel 120_N to the otherchannels 120_1-120_(N−1). In several embodiments, the interferencereduction circuits 122_1-122_N can be implemented by a bidirectionallow-pass filter comprising an inductor L1 and two capacitors C1 and C2,or a bi-directional notch filter comprising an inductor L2 and acapacitor C3 as shown in FIG. 2 (a)-(b), or a bidirectional band-passfilter with tunable frequency response, or the interference reductioncircuits 122_1-122_N can be implemented by an amplifier for providingreverse isolation to suppress the leakage of local oscillating signalfrom a mixer, a conductor line or a transmission line as shown in FIG. 3(a)-(c), the intrinsic frequency response of a conductor line ortransmission line can provide particular suppression at particularfrequencies.

When frequencies of part of the oscillation signals LO1-LON satisfy aspecific condition, the mixer 124_1 may be influenced by the otheroscillation signals due to the coupling effect if no interferencereduction circuit is applied. By using the interference reductioncircuit 122_2 positioned before the mixer 124_2 of the channel 120_2,the harmonic of the oscillating signal LO2 can be filtered or isolatedfrom the channel 120_1, thereby the mixer 124_1 will not be interferedby the oscillating signal LO2 as shown in FIG. 4. The specific conditionmay be that an Nth harmonic of the frequency of the oscillating signalLO1 is substantially equal to a Mth harmonic of the frequency of theoscillating signal LO2 (e.g. LO1=4 GHz, LO2=3 Gz); or the specificcondition may be that a summation of harmonics of the frequencies of theoscillation signals is equal to a frequency of an IF signal as shown inFIG. 5. In the example (a)-(c) shown in FIG. 5, when the harmonics ofthe oscillation signals satisfy the equations: −1*f3+2*f2−1*f1=IF, or−1*f3+4*f2−3*f1=IF, or −1*f3−2*f2+3*f1=IF (f1, f2 and f3 are frequenciesof the L01-L03, respectively), the harmonics of the oscillation signalsLO2 and LO3 may affect the operations of the mixer 124_1 if nointerference reduction circuit is applied, that is the channels 120_2and 120_3 are regarded as aggressor channels and the channel 120_1 isregarded as a victim channel if no interference reduction circuit isapplied, therefore, by using the interference reduction circuits 122_2and 122_3 shown in FIG. 5, the harmonic of the oscillation signals LO2and LO3 can be filtered or isolated from the channel mixer 124_1.

FIG. 6 shows the detailed structure of the amplifier module 110according to one embodiment of the present invention. As shown in FIG.6, the amplifier module 110 comprises at least six amplifiers 612, 614,622, 624, 632 and 634. These amplifiers are arranged to selectivelycouple the signal V1 to the channel 120_1 or 120_2, and to selectivelycouple the signal V2 to the channel 120_1 or 120_2. For example, whenthe signals V1 and V2 are required to be processed by the channels 120_1and 120_2, respectively, the amplifiers 612, 614, 622 and 624 areenabled, and the amplifiers 632 and 634 are disabled; when the signal V1is required to be processed by the channel 120_2, the amplifiers 612,632 and 624 are enabled, and the amplifiers 622, 634 and 614 aredisabled; and when the signal V2 is required to be processed by thechannel 120_1, the amplifiers 622, 634 and 614 are enabled, and theamplifiers 612, 632 and 624 are disabled.

FIG. 7 shows the detailed structure of the amplifier module 110according to another embodiment of the present invention. As shown inFIG. 7, the amplifier module 110 comprises at least four amplifiers 702,704, 706 and 708. These amplifiers are arranged to selectively couplethe signal V1 to the channel 120_1 or 120_2, and to selectively couplethe signal V2 to the channel 120_1 or 120_2. For example, when thesignals V1 and V2 are required to be processed by the channels 120_1 and120_2, respectively, the amplifiers 702 and 708 are enabled, and theamplifiers 704 and 706 are disabled; and when the signals V1 and V2 arerequired to be processed by the channels 120_2 and 120_1, respectively,the amplifiers 704 and 706 are enabled, and the amplifiers 702 and 708are disabled.

Please refer to FIG. 8, which is a diagram illustrating a system 800according to one embodiment of the present invention. As shown in FIG.8, the system 800 comprises an antenna 802, an amplifier module 810 anda plurality of channels (in this embodiment, there are two channels 820and 830), where the channel 820 comprises an interference reductioncircuit 822 and a mixer 824; and the channel 830 comprises twosub-channels, where one sub-channel comprises an interference reductioncircuit 832 and a mixer 834, and the other sub-channel merely comprisesa mixer 844. In this embodiment, the mixers 834 and 844 within thechannel 830 use the oscillation signals LO2 with the same frequency, andonly one of the mixers 834 and 844 can receive the oscillating signalLO2 at the same time (i.e. only one of the sub-channels is enabled togenerate the IF signal).

In this embodiment, the system 800 is a receiver or a transceiver, andis arranged to receive RF signals from the antenna 802 to generate atleast one IF signal for further processing. In detail, the amplifiermodule 810 receives signals from an antenna to generate two RF inputsignals Vin1-Vin2, and the mixers 824 mixes the RF input signal Vin1with oscillating signal LO1 to generate the IF signal Vout1, and one ofthe mixers 834 and 844 within the channel 830 mixes the RF input signalVin2 with the oscillating signal LO2 to generate the IF signal Vout2.

In the system 800 shown in FIG. 8, the interference reduction circuit832 is arranged to reduce harmonics from the mixer 834 to the channel820, and the interference reduction circuit 832 can be implemented byany one of the circuits shown in FIG. 2 and FIG. 3. In the embodimentshown in FIG. 8, although the interference reduction circuit 832 canreduce harmonics from the mixer 834 to the channel 820, it may degradethe performance of the mixer 834. Therefore, the channel 830 shown inFIG. 8 has two sub-channels to selectively process the RF input signalVin2. In detail, when the oscillating signal LO2 satisfies the specificcondition and the harmonics of the oscillating signal LO2 may affect themixer 824, the mixer 834 is selected to receive the oscillating signalL02, and the RF input signal Vin2 is processed by the interferencereduction circuit 832 and the mixer 834 to generate the IF output signalVout2. On the other hand, when the oscillating signal LO2 does notsatisfy the specific condition, that is the harmonics of the oscillatingsignal LO2 may not affect the mixer 824, in order to have the betterperformance, the mixer 844 is selected to receive the oscillating signalL02, and the RF input signal Vin2 is processed by the mixer 844 togenerate the IF output signal Vout2. In this embodiment, the specificcondition may be that an Nth harmonic of the frequency of theoscillating signal LO1 is substantially equal to a Mth harmonic of thefrequency of the oscillating signal LO2 (e.g. LO1=4 GHz, LO2=3 Gz); orthe specific condition may be that a summation of harmonics of thefrequencies of the oscillation signals is equal to a frequency of an IFsignal as shown in FIG. 5.

Briefly summarized, in the multi-mixer system of the present invention,by using the interference reduction circuit between the amplifier moduleand the mixer, harmonics of a local oscillating signal can be filteredor isolated from the other channels, and the performance of the mixerscan be improved.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A multi-mixer system, comprising: an amplifiermodule, for receiving signals from at least an antenna to generate atleast a first radio frequency (RF) input signal and a second RF inputsignal; and a first channel coupled to the amplifier module, wherein thefirst channel comprises a first mixer and a first interference reductioncircuit configured between the amplifier module and the first mixer, andthe first channel is used to receive the first RF input signal togenerate a first mixed signal; and a second channel coupled to theamplifier module, wherein the second channel is used to receive thesecond RF input signal to generate a second mixed signal, the secondchannel comprises a first sub-channel and a second sub-channel, thefirst sub-channel comprises a second mixer and a second interferencereduction circuit configured between the amplifier module and the secondmixer, and the second sub-channel comprises a third mixer; wherein onlyone of the first sub-channel and the second sub-channel is enabled togenerate the second mixed signal, and when an oscillating signal used bythe second mixer or the third mixer satisfies a specific condition, thefirst sub-channel is enabled to generate the second mixed signal, andthe second sub-channel is disabled; and when the oscillating signal usedby the second mixer or the third mixer does not satisfy the specificcondition, the first sub-channel is disabled, and the second sub-channelis enabled to generate the second mixed signal.
 2. The multi-mixersystem of claim 1, wherein oscillation signals used by the second mixerand the third mixer have a same frequency.
 3. The multi-mixer system ofclaim 1, wherein only one of the first sub-channel and the secondsub-channel is enabled to generate the second mixed signal.
 4. Themulti-mixer system of claim 1, wherein no interference reduction circuitis configured between the amplifier module and the third mixer of thesecond sub-channel.
 5. The multi-mixer system of claim 4, wherein thefirst mixer and the first interference reduction circuit of the firstchannel are always used to generate the first mixed signal; and only oneof the first sub-channel and the second sub-channel is enabled togenerate the second mixed signal.
 6. The multi-mixer system of claim 1,wherein the specific condition is that an Nth harmonic of the frequencyof the oscillating signal used by the second mixer or the third mixer issubstantially equal to a Mth harmonic of a frequency of anotheroscillating signal used by a mixer within another channel.
 7. Themulti-mixer system of claim 1, wherein the specific condition is that asummation of a harmonic of the frequency of the oscillating signal usedby the second mixer or the third mixer and at least one of a harmonic ofa frequency of another oscillating signal used by another channel isequal to a frequency of a mixed signal generated by the another channel.8. The multi-mixer system of claim 1, wherein one of the firstinterference reduction circuit and the second interference reductioncircuit is arranged to reduce harmonics from the mixer within a samechannel to other channels.
 9. The multi-mixer system of claim 1, whereinone of the first interference reduction circuit and the secondinterference reduction circuit is a low-pass filter, a band-pass filteror a notch filter.
 10. The multi-mixer system of claim 1, wherein one ofthe first interference reduction circuit and the second interferencereduction circuit is a bidirectional low-pass filter, a bidirectionalband-pass filter or a bidirectional notch filter.
 11. The multi-mixersystem of claim 1, wherein one of the first interference reductioncircuit and the second interference reduction circuit is an amplifierfor providing reverse isolation.
 12. A method for reducing interferencewithin a multi-mixer system, wherein the multi-mixer system comprises:an amplifier module, for receiving signals from at least an antenna togenerate at least a first radio frequency (RF) input signal and a secondRF input signal; and a first channel coupled to the amplifier module,wherein the first channel comprises a mixer and receives the first RFinput signal to generate a first mixed signal; and a second channelcoupled to the amplifier module, wherein the second channel is used toreceive the second RF input signal to generate a second mixed signal,the second channel comprises a first sub-channel and a secondsub-channel, the first sub-channel comprises a second mixer, and thesecond sub-channel comprises a third mixer; and the method comprises:reducing an interference of a first oscillating signal between theamplifier module and the first mixer; selectively choosing one of thefirst sub-channel and the second sub-channel to generate the secondmixed signal; and selectively reducing or not reducing an interferenceof second oscillating signals used by the second channel, wherein if thefirst sub-channel of the second channel is enabled, reducing theinterference of the second oscillating signal, and the second mixer ofthe first sub-channel generates the second mixed signal; and if thesecond sub-channel of the second channel is enabled, not reducing theinterference of the second oscillating signal, and the third mixer ofthe first sub-channel generates the second mixed signal.
 13. The methodof claim 12, wherein the second oscillation signals used by the secondmixer and the third mixer have a same frequency.
 14. The method of claim12, wherein the step of reducing the interference of the firstoscillating signal between the amplifier module and the first mixercomprises: always reducing the interference of the first oscillatingsignal to make the first mixer generate the first mixed signal.
 15. Themethod of claim 12, wherein the step of selectively choosing one of thefirst sub-channel and the second sub-channel to generate the mixedsignal comprises: when the oscillating signal used by the second mixeror the third mixer satisfies a specific condition, enabling the firstsub-channel to generate the mixed signal, and disables the secondsub-channel; and when the oscillating signal used by the second mixer orthe third mixer does not satisfy the specific condition, disabling thefirst sub-channel, and enabling the second sub-channel to generate thesecond mixed signal.
 16. The method of claim 15, wherein the specificcondition is that an Nth harmonic of the frequency of the oscillatingsignal used by the second mixer or the third mixer is substantiallyequal to a Mth harmonic of a frequency of another oscillating signalused by a mixer within another channel.
 17. The method of claim 15,wherein the specific condition is that a summation of a harmonic of thefrequency of the oscillating signal used by the second mixer or thethird mixer and at least one of a harmonic of a frequency of anotheroscillating signal used by another channel is equal to a frequency of amixed signal generated by the another channel.